PARP3 is a promoter of chromosomal rearrangements and limits G4 DNA

Chromosomal rearrangements are essential events in the pathogenesis of both malignant and nonmalignant disorders, yet the factors affecting their formation are incompletely understood. We developed a zinc finger nuclease translocation reporter (ZITR) and screened for factors that modulate rearrangements in human cells. We identified UBC9 and RAD50 as suppressors and 53BP1, DDB1, and PARP3 as promoters of chromosomal rearrangements across human cell types. We focused on poly(ADP)ribose polymerase 3 (PARP3) as it is dispensable for murine viability and has druggable catalytic activity. We found that PARP3 regulated G quadruplex (G4) DNA in response to DNA damage, which suppressed repair by nonhomologous end-joining and homologous recombination. Chemical stabilization of G4 DNA in PARP3-/- cells led to widespread DNA double-strand breaks and synthetic lethality. We propose a model in which PARP3 suppresses G4 DNA and facilitates DNA repair by multiple pathways. Overall design: RNA-seq was performed on WT and PARP3-/- A549 cells with vehicle treatment or treatment with 1 micromolar pyridostatin. All conditions were performed in biological triplicate.